Actually, in my experience with repeaters, 375W output on 146 MHz will
definitely make RG213/U warm, and can make 9913 warm as well. That power
level will literally "melt" RG8X (mini-8). Of course, around repeaters only
double-shielded (or 100% shielded, such as hardline, heliax, semi-rigid
coaxitube, etc) should be used.
Solder isn't 60% lead, it's normally 60% tin and 40% lead, and eutectic
solder used for PCB assembly is 63% tin, 37% lead. Going to 96/4 Sn/Ag (4%
silver solder) improves conductivity very marginally; it's main advantage is
elminating lead content, which is poisonous.
PL-259's normally should not be used in repeater service, simply because
they are single-shielded and not constant impedance. If you're using Type
N, Type C, or other "repeater environment" connectors, there shouldn't be a
problem, as these are double-shielded, constant-impedance types.
A 1.3 VSWR, although undesirable in a repeater system because any reflected
current at all can create desensitization, is not excessive by any means.
But the DB products 4-pole should be capable of better, if tuned to the
repeater's TX frequency. DB products, Celwave and others make antenna
matching units for the 136 to 174 MHz band, which will trim up an antenna to
perfect 1.0 VSWR at any one specific frequency, and are site-tunable using
piston trimmer caps. Such a tuner should be installed between the duplexer
and the antenna's transmission line and adjusted for VSWR=1.0 as measured
between the duplexer and the tuner.
However, VSWR = 1.3 should not create any additional jumper cable heating.
73 de Steve, WB2WIK/6
> Hi!
>
> ANY time an electrical conductor gets warm, it is due to resistance. You
> have a high resistance joint either in that coaxial jumper or in one or
> both
> of the connectors. I'd guess it's a "cold" solder joint or joints.
> Sometimes, you can measure the thing with an ohmmeter and it will show "Ø"
>
> ohms, yet it will act squirrely at radio frequencies.
>
> First replace the jumper. If that does not stop the heating, replace the
> connectors on the other coaxes/hardlines. If you have a contact
> thermometer
> you could hold it on the various parts of the joints to see where the heat
> is
> originating, but 99:1, it's coming from one of the joints which is faulty.
>
> The reason the meter readings vary is because of additional resistance or
> inductance introduced into the feedline by your various hookups. If there
>
> was no change in the impedance or resistance, the meter readings would not
>
> change.
>
> Be sure if you use a soldering iron, that it's big enough for the job.
> This
> way the solder gets melted properly. Remember, solder is 60% lead and
> lead
> is a pretty high resistance metal. That's why in high current
> applications,
> like plate tank coil connections silver solder is often used.
>
> Good Luck,
>
> Mike Lonneke
> WØYR
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